miler

noun[in compounds]2

1. •
   An athlete or a horse who specializes in running races of one mile, or a specified number of miles.

   • But the master himself was an old Oxford miler, who could still bear it better than I; nay, as I flagged and stumbled, I heard him pounding steadily behind. — 1905
2. •
   A race whose length is the specified number of miles.

   • I ran an eight-miler on Sunday and I'm still feeling sore.